The electronics field, and particularly the electronic component field, is constantly seeking to improve devices such as capacitors employed in electronic circuits.
There is a particular need for dielectric materials for use in capacitors which exhibit low dissipation factors (or high Q values) at the operating frequencies and have a low temperature coefficient which preferably can be altered depending upon composition to give you a negative, positive or zero temperature coefficient (NPO materials). It is preferred that these materials have as high a dielectric constant as possible in a temperature range of from -55.degree. C. to 125.degree. C. However, as Q increases, generally, the dielectric constant decreases such that the attainment of high dielectric constants and high Q has been mutually unattainable. Typical presently available ceramic compositions which have Q values up to about 1,000 at 1 MHz exhibit dielectric constants of only about 20 and temperature coefficients of [.+-.0 to 1000].times.10.sup.-6 /.degree.C.
It is therefore desirable to develop a dielectric material having values of Q of at least 500 at 1 MHz while attaining dielectric constants of at least 100 at typical operating temperatures.
Of further interest for the commercial manufacture of such dielectric materials, is that the material be sinterable at temperatures of preferably less than 1,000.degree. C. This reduction in sintering temperature not only saves cost in the sintering operation, but also allows less expensive electrodes to be applied to the ceramic material, particularly when employed in a multilayer ceramic capacitor having electrodes between layers which are incorporated prior to sintering.
Dielectric materials based upon lead niobate and including compositions having lead zinc niobate or other substituted lead niobates have been reported. For example reference can be made to U.S. Pat. Nos. 3,600,652; 4,339,544 and 4,379,319. However, the compositions reported in these patents differ from the subject compositions and capacitors made therefrom have substantially different properties.